In the past, there has been extensive description in the patent and other technical literature of electrophoretic migration imaging processes. A description of electrophoretic migration imaging processes may be found in U.S. Pat. Nos. 2,758,939 by Sugarman issued Aug. 14, 1956; 2,940,847; 3,100,426, 3,140,175 and 3,143,508, all by Kaprelian; 3,384,565, 3,384,488 and 3,615,558, all by Tulagin et al; 3,384,566 by Clark; 3,383,993 by Yeh; and U.S. Pat. No. 3,976,485 by Groner.
In each of the foregoing electrophoretic migration imaging processes an imaging layer comprising electrically photosensitive particulate material is subjected to the influence of an electric field and exposed to an image pattern electromagnetic radiation to which the electrically photosensitive material is sensitive. The electrically photosensitive material is caused to imagewise migrate electrophoretically in the layer to form a record of the imaging electromagnetic radiation.
In any case, regardless of the particular electrophoretic migration imaging process employed, it is apparent that an essential component of any such process is the electrically photosensitive material. And, of course, to obtain an easy-to-read visible image it is important that the electrically photosensitive material be colored, as well as electrically photosensitive. Accordingly, there exists a continuing effort to find materials which possess both useful levels of electrical photosensitivity and which exhibit good colorant properties. Thus, various types of electrically photosensitive materials are disclosed for use in electrophoretic migration imaging processes.
Up to now, useful electrically photosensitive colorant materials for electrophoretic migration imaging have been selected from known classes of photoconductive materials which may be employed in conventional photoconductive elements, e.g., photoconductive plates, drums, or webs used in electrophotographic office-copier devices. For example, both Sugarman and Kaprelian in the above-referenced patents state that electrically photosensitive materials useful in electrophoretic migration imaging processes may be selected from known classes of photoconductive materials. Also, the phthalocyanine pigments described as a useful electrically photosensitive material for electrophoretic imaging processes in U.S. Pat. No. 3,615,558 by Tulagin et al. have long been known to exhibit useful photoconductive properties.